Time measurement in a communications system, a communications system and a receiver for use in such a system

Abstract

A communications system includes apparatus for generating a succession of time message signals, a central station having a transmitter for transmitting the time message signals, at least a first receiver for receiving the time message signals and timer circuits for determining the real time of receipt of each time message signal. Each time message signal is representative of the real time of receipt, by the first receiver, of a preceding time message. The first receiver includes a clock for providing the first receiver with an internal time signal. The clock is reset upon receipt of a first time message signal and is advanced, upon receipt of a subsequent time message signal, by the real time indicated by the subsequent time message signal.

What we claim is: 
     
       1. A communications system comprising: means for generating a succession of time message signals;   a central station having means for transmitting said time message signals;   at least a first receiver for receiving said time message signals; and   timing means for determining the real time of receipt of each time message signal,   said communications system being characterized in that each said time message signal is representative of the real time of receipt by said first receiver of a preceding time message signal,   and in that said first receiver comprises: clock means for providing said first receiver with an internal time signal;   means for resetting said clock means upon the receipt of a first time message signal; and   means for advancing said clock means, upon receipt of a subsequent time message signal, by the real time indicated by said subsequent time message signal.     
     
     
       2. A communications system according to claim 1, wherein said clock means comprises: a counter having an output for providing said internal time signal; and   means for incrementing the contents of said counter so that the contents of the counter represent a time interval.   
     
     
       3. A communications system according to claim 2, wherein said means for advancing said clock means comprises means for adding a value representative of the real time indicated by said subsequent time message signal to the contents of said counter. 
     
     
       4. A communication system according to claim 1, wherein said timing means comprises: a second receiver for receiving said time message signals; and   means for determining the real time of receipt of each time message signal by said second receiver.   
     
     
       5. A communications system according to claim 4, wherein said means for determining the real time of receipt of each time message signal comprises a real time clock. 
     
     
       6. A communications system according to claim 4, wherein said means for determining the real time of receipt of each time message signal comprises a third receiver for receiving real-time messages. 
     
     
       7. A communications system according to claim 1, wherein said timing means comprises means for generating a zone-code for inclusion in said time message signals, said zone-code being indicative of the transmission coverage area of said central station. 
     
     
       8. A communications system according to claim 7, wherein said first receiver comprises means for assuring that said first and said subsequent time-message signals include the same zone-code. 
     
     
       9. A receiver for use in a communication system in which a succession of time message signals are transmitted by a central station, said receiver comprising: means for receiving said time message signals;   clock means for providing said first receiver with an internal time signal;   means for resetting said clock means upon the receipt of a first time message signal; and   means for advancing said clock means, upon receipt of a subsequent time message signal, by the real time indicated by said subsequent time message signal.   
     
     
       10. A receiver according to claim 9, wherein said clock means comprises: a counter having an output for providing said internal time signal; and   means for incrementing the contents of said counter so that the contents of the counter represent a time interval.   
     
     
       11. A receiver according to claim 10, wherein said means for advancing said clock means comprises means for adding a value representative of the real time indicated by said subsequent time message signal to the contents of said counter. 
     
     
       12. A receiver according to claim 9 wherein said time message signals comprise a zone-code indicative of the transmission coverage area of said central station, said receiver further comprising means for assuring that said first and said subsequent time-message signals include the same zone-code. 
     
     
       13. A communications system according to claim 2, wherein said timing means comprises: a second receiver for receiving said time message signals; and   means for determining the real time of receipt of each time message signal by said second receiver.   
     
     
       14. A communications system according to claim 3, wherein said timing means comprises: a second receiver for receiving said time message signals; and   means for determining the real time of receipt of each time message signal by said second receiver.   
     
     
       15. A communications system according to claim 13, wherein said means for determining the real time of receipt of each time message signal comprises a real time clock. 
     
     
       16. A communications system according to claim 13, wherein said means for determining the real time of receipt of each time message signal comprises a third receiver for receiving real-time messages. 
     
     
       17. A communications system according to claim 14, wherein said means for determining the real time of receipt of each time message signal comprises a third receiver for receiving real-time messages. 
     
     
       18. A receiver according to claim 10, wherein said time message signals comprise a zone-code indicative of the transmission coverage area of said central station, said receiver further comprising means for assuring that said first and said subsequent time-message signals include the same zone-code. 
     
     
       19. A communications system comprising: means for generating a succession of time message signals;   a central station including a transmitter for transmitting the time message signals;   a first pager including a first receiver for receiving the time message signals transmitted by said central station;   said means for generating a succession of time message signals including a second receiver for receiving the transmitted time message signals;   said means for generating a succession of time message signals further including means for generating a first time message signal representing real time and means responsive to said second receiver for generating succeeding time message signals representing the real time at which an immediately preceding one of said succession of time message signals was transmitted by said transmitter;   said pager including, a counter which is reset upon reception of said first time message signal by said first receiver,   means for incrementing the counter so that its contents represent the passage of time, and   means for adding to the contents of said counter a time value in the next succeeding time message signal received by said first receiver.     
     
     
       20. A communications system as claimed in claim 19, wherein said means for generating a succession of time message signals includes a third receiver for receiving indications of real time transmitted from an absolute time reference source.